1. Field of the Invention
The invention relates to a hybrid vehicle, and particularly to a hybrid vehicle that has an internal combustion engine and electric motor to transmit power to a drive wheel through a power transmission mechanism, and that is capable of setting a motor travel mode so as to be able to travel using only the electric motor as a drive power source.
2. Description of the Related Art
In recent years, hybrid vehicles have received a lot of attention as environmentally-friendly automobiles. In addition to an internal combustion engine driven by fuel, a hybrid vehicle has, as the drive power sources, an electric storage device composed of a secondary battery, and a generator that generates vehicle drive power by receiving electricity from the electric storage device.
Such a hybrid vehicle carries out travel control by selecting a mode in which the hybrid vehicle travels using only the output of the generator (electric vehicle (EV) mode) in an operating range, such as during low-speed running at startup where the internal combustion engine does not function efficiently, and selecting a travel mode in which the internal combustion engine is started up when the vehicle speed rises and thereby traveling powers of both the internal combustion engine and the generator can be used (hybrid vehicle (HV) mode).
Particularly, a so-called “plug-in hybrid vehicle” that has an external charging function for charging a secondary battery by means of a commercial power source has recently been developed. Because this hybrid vehicle can travel in the EV mode for comparatively a long time, the internal combustion engine can be deactivated for a longer period of time, and therefore efficiency can be improved.
Incidentally, a power transmission device that transmits power from the internal combustion engine to a drive wheel has a planetary gear mechanism and the like for switching the power between the EV mode and the HV mode of the internal combustion engine and the generator, and the planetary gear mechanism and the like need to be lubricated by lubricant oil.
However, because mainly a crankshaft functioning as an output shaft of the internal combustion engine drives an oil pump supplying the lubricant oil to the planetary gear mechanism and so on, the oil pump is not driven during EV mode travel in which the internal combustion engine is stopped, causing an unlubricated state in the planetary gear mechanism and so on.
To prevent an unlubricated state in the planetary gear mechanism, a hybrid vehicle is available in which the stopping time during which an internal combustion engine is stopped is measured during the EV mode travel and then the internal combustion engine is started up (complete explosion) at the time of the subsequent travel when the measured time exceeds a constant time period (see Japanese Patent Application Publication No. H6-165309 (JP-A-6-165309), for example). According to this hybrid vehicle, because the internal combustion engine can be operated regularly during the EV travel, an oil pump can be driven regularly to supply lubricant oil to the planetary gear mechanism, and thereby deterioration of lubricity of the planetary gear mechanism and so on can be prevented.
Furthermore, a hybrid vehicle is available which, when the internal combustion engine is stopped for a long time during the EV travel, carries out control called motoring based on a cumulative value of a stop history of the internal combustion engine (the travel distance and so on that are obtained when the internal combustion engine is being stopped) to drive a motor coupled to a crankshaft without exploding the internal combustion engine, thereby rotates the crankshaft to drive the oil pump, and thereafter resets the cumulative value of the stop history of the internal combustion engine (see Japanese Patent Application Publication No. 2002-349405 (JP-A-2002-349405), for example).
However, because the hybrid vehicle described in JP-A-6-165309 measures the stopping time of the internal combustion engine during the EV travel in order to completely explode the internal combustion engine in the subsequent travel if the measured time exceeds the constant time period, when the internal combustion engine is stopped for a long time during the EV travel, eventually the fuel is injected to the internal combustion engine, degrading fuel efficiency.
Moreover, because the measured stopping time of the internal combustion engine is accumulated, there is no device for resetting the cumulative value of the measured time when a driver executes a drive termination operation, that is, when the driver turns a power switch off. Therefore, when the driver executes a drive start operation, that is, when the driver turns the power switch on to bring the hybrid vehicle into a travelable state, there is a possibility that the cumulative value of the measured stopping time of the internal combustion engine exceeds the constant time period during the EV travel. As a result, the fuel is injected into the internal combustion engine, deteriorating the fuel. Furthermore, in the hybrid vehicle described in JP-A-2002-349405, the crankshaft is rotated by carrying out motoring without completely exploding the internal combustion engine during the EV travel. For this reason, the motor reaction force is transmitted to a drive wheel, degrading the drivability. In order to prevent the transmission of the motor reaction force to the drive wheel, control needs to be performed to cancel the motor reaction force.